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NIH selects louse genome research to improve human health

December 7, 2005

Photo of Barry Pittendrigh using a microscope in the lab

Dr. Barry Pittendrigh

WEST LAFAYETTE, Ind. - Head lice often are the bane of schoolchildren, but it's another variety of the insect - body lice - that carries some of the most infamous and deadly diseases that have plagued people for centuries.

A team of researchers led by Purdue University insect geneticist Barry Pittendrigh and University of Massachusetts environmental toxicologist John Clark has the green light to take the first steps toward sequencing the complete body louse genome.

The ultimate aim is to invent new pest control methods to prevent the spread of diseases, such as relapsing fever, trench fever and typhus. The Centers for Disease Control and Prevention (CDC) classifies typhus as a bioterrorism agent.

Information gained from the sequencing project also will provide clues on how the grain-of-rice sized insects pass on to people and other animals infection-causing organisms.

"If we have a relatively complete louse genome, we can do experiments necessary to discover how lice can digest human blood and transmit disease," said Pittendrigh, a Purdue associate professor of entomology and lead author of the proposal for the National Institutes of Health-funded genome project. "The more we learn about the biochemical workings of these tiny creatures, the greater our chance of impacting issues associated with human health."

Photo of body lice

Body lice, pictured at different stages of development, carry a number of diseases. Researchers led by Barry Pittendrigh of Purdue University and John Clark of the University of Massachusetts are beginning an NIH-supported project to sequence and map the body lice genome in an effort to develop better methods to control the six-legged pest. (Photo courtesy of John Clark, Kyong Sup Yoon and Joseph P. Strychartz, University of Massachusetts)

Body lice spread epidemic typhus by transmitting an organism called Rickettsia prowazekii. The disease, characterized by a high fever and rash, usually occurs in areas where people have poor hygiene, especially in developing countries. It also happens in crowded places such as jails. The disease has a 10 percent to 60 percent fatality rate, and experts say that the disease-causing organism could be used by terrorists as a biological weapon.

Pittendrigh's research team already has collected preliminary information on the lice genome, which will be sent to one of the five centers that are part of the NIH-National Human Genome Research Institute's Large-Scale Sequencing Network. The network facility assigned to the project will do the actual gene sequencing.

Although in earlier research Pittendrigh identified some body lice genes that are involved in the digestion of their human blood meal and their response to bacteria, the researcher said only a small portion of the needed knowledge has been uncovered.

"Dr. Pittendrigh's louse project is an excellent illustration of the value of investing research dollars in promising new areas delving into the biology of disease-carrying insects," said Jeanne Romero-Severson, director of the University of Notre Dame-based Indiana Center for Insect Genomics, which provided seed money for a small-scale louse project through the Indiana 21st Century Research and Technology Fund.

"Currently there are no complete genomes of this type of insect, mainly because most disease-carrying species have such large genomes," Pittendrigh said. "Body lice have the smallest insect genome known to date."

Spencer Johnson, a Texas A&M geneticist, discovered the small size of the louse genome while collaborating with Pittendrigh and Clark on the proposal to the NIH for the body louse genome project.

The louse genome sequencing continues the national genome institute's emphasis on using comparative genomic sequencing analysis to understand the structure and function of the human genome and the biological processes involved in human diseases, according to the NIH.

The body louse genome is one of seven non-mammalian organisms chosen this year for the program and one of three targeted for a high-quality sequence. The NIH said the louse was included in this group because it is one of the organisms that can reveal a large amount of information about how biology has evolved over hundreds of thousands of years, including development of the human genome.

The combined louse genome and human genome knowledge will shed light on ways to relieve people of lice and their diseases, Pittendrigh said. Researchers and health-care workers need new ways to deal with human infestations by the six-legged, yellowish pests that have become resistant to current pesticides.

"Detection, treatment and prevention could be improved with a greater understanding of the molecular biology that allows lice to use the human body as a living habitat," he said. "It's imperative that new molecular targets are discovered to aid in development of novel control methods."

Clark maintains a special line of lice, which the research team will use for their genome work. Most lice can live only on human blood, but Clark discovered a special membrane that allows the lice to obtain a blood meal without a direct interaction with a human being. This has allowed him to maintain colonies of very genetically uniform lice.

"Dr. Clark's unique rearing facilities for head and body lice are absolutely critical to our efforts on the body louse genome and for understanding the genomics of head lice," Pittendrigh said.

The genetic uniformity will simplify collection of small chunks of lice DNA to be used for the actual sequencing. After sequencing all the pieces, they will be fitted back together to form a complete genome map.

"Once this genome is completed, we will be able to compare it to the genomes of other similar disease-carrying animals, which will help determine the transmission mechanisms of other diseases," Pittendrigh said.

The other researchers involved with the louse genome project are Si Hyeock Lee of Seoul National University, and Gregory Dasch of the CDC.

Indiana's 21st Century Research and Technology Fund and the Indiana Center for Insect Genomics have provided funding for the preliminary work on the louse genome. The NIH-National Institute of Allergy and Infectious Disease supported Clark's studies on louse rearing and louse resistance to control methods.

Writer: Susan A. Steeves, (765) 496-7481, ssteeves@purdue.edu

Source: Barry Pittendrigh, (765) 494-7730, pittendr@purdue.edu

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
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